Oxygen sensors (or exhaust constituent sensors) have been used for many years in automotive vehicles to sense the presence of constituents (e.g., oxygen, hydrocarbons, nitrous oxides) in an exhaust gas flow and to sense and/or signal, for example, when an internal combustion engine switches from rich to lean or lean to rich operation.
Because automotive oxygen sensors are required to be positioned within the exhaust gas flow and be mounted within a component of the vehicle exhaust system, oxygen sensor designs must provide for durable sensors and secure mounting. The oxygen sensor is exposed to and must be able to withstand vibration and jarring such as would occur from vehicle operation, or from shock produced from the occasional stone or other small road debris that may happen to be thrown at the sensor, for example, by the vehicle's tires.
Current oxygen sensor design limitations severely limit positioning and configuration of oxygen sensors within an exhaust system. Foremost among these limitations is the requirement that an oxygen sensor be mounted on a flat surface. This is necessitated by the fact that sensors require a complete seal around their mountings for proper operation of the sensors and to avoid negative effects on emissions and performance. Typically, the sensors are mounted utilizing a fitting that is drilled and fabricated in a convenient section of exhaust tubing.
Currently, primary methods for fabricating bushings include use of cold heading, screw machining, or powdered metal for independent fabrication of a bushing. The prefabricated bushing is inserted into a hole pierced in the exhaust component, and the bushing is welded using metal inert gas (MIG) welding or projection welding. However, welding of prefabricated bushings to exhaust system components has produced a number of serious problems in the art, including weld spatter in threads, thread distortion, weld skips, or voids, created by welding heat. These defects usually translate to excess scrap and high rework costs.
Accordingly, there remains a need for an arrangement of an oxygen sensor within an exhaust system of an internal combustion engine that allows for greater flexibility in placement and minimized exposure to damage.